1. Field of the Invention
The present invention relates to an image reading apparatus, and particularly to management of image data read from an original document in an image reading apparatus.
2. Description of the Related Art
In recent years, as network technology becomes widespread, document data generated by scanning an original document comes to be used for various uses (data transmission, print output via a network, etc.).
Besides, as a color printer or a color digital copier becomes widespread, colorization of document data has been advanced rapidly.
The colorization of document data becomes indispensable in various scenes such as presentation, and has many merits, however, it has also a defect that an increase in the amount of information is caused. Handling the document data whose capacity is increased by the colorization imposes a large load on a client PC or a network.
For example, in the case where an original document is read in color by a related art image reading apparatus, it is general to use a color sensor in which primary color filters of RED, GREEN and BLUE are arranged on a light receiving surface, for example, a 3-line CCD sensor in which the filters are arranged on light receiving surfaces of respective line sensors.
In the case where an original document of A4 size (210 mm×297 mm) is read at a resolution of 600 dpi by an image reading apparatus using the related art 3-line CCD sensor as stated above, the capacity of image data becomes 105 MByte (35 MByte×RGB), and in the case where an original document of A3 size (420 mm×297 mm) is read, the capacity of data becomes as large as 210 MByte.
Then, in order to suppress the increase in the capacity of document data due to the colorization of the document data, a compression technique of the document data is required.
With respect to the compression technique of the document data, there is known a method in which a rough division is made into an image portion, such as a photograph, generated at a halftone and a line drawing portion including a character, a thin line and the like, and the image portion and the line drawing portion are separately compressed, so that the compression ratio of the document data is increased without impairing the information of the original image (JP-A-2-274174).
However, with the colorization of document data in recent years, the document data is used for many purposes, and therefore, not only the reduction of data, but also a suitable and flexible processing of monochrome information and color information is required.